For years, people have been playing games such as chess, checkers, scrabble, monopoly, etc. which utilize game boards and game pieces which are positioned on a board. The position or identity of any game piece on the board was determined by human observation, since no other system existed. If one desired to record the position of each game piece as a game progressed, one would have to perform such an operation manually. There are some particular board games, in particular, chess, where it is advantageous to record all game piece positions throughout the game, so that the game can be studied by skilled players as well as by other players of lesser skill, so they can improve their skill. For this reason, the description of the invention will be in terms of chess and utilize a chess board and chess pieces. However, the invention can be applied to other board games with varying degrees of advantage.
Serious players of the game of chess find it important to record every move of every game so that the game can be re-played for the purpose of detecting and correcting mistakes and learning how to improve their playing ability in future chess matches. When the game is played on a standard chess board, the moves are recorded manually. This method of recording moves has a significant drawback, namely that it is relatively slow. There is a type of chess game known as "speed chess" where each player is encouraged to make his move as soon as possible after an opponent makes their move. In this type of game, it is not possible to manually record the moves. When such a game is played by the leading players in the world, other high level players would like the opportunity to study such a game, but are denied the opportunity because the game cannot be manually recorded.
Another disadvantage of a "standard" chess game is that the number of spectators that can observe the actual match is very limited, and often spectators are denied the privilege of watching for fear of disturbing the players. Such games are usually recreated on a secondary chess board and displayed for an audience in another room or at a remote location. There is a definite need for a chess set which would eliminate these deficiencies and allow a game to be automatically recorded, no matter how fast the players move the pieces, and that would allow a large audience to observe the game without disturbing the players.
Several years ago, a board was invented which contained, among other features, a switch under each square, and an element in each piece which activated the switch when a piece was on that square. With this system, the board could detect which squares contained a chess piece and which squares were vacant. Unfortunately, the board could not identify the rank of the piece that was on each square. In order to compensate for this piece recognition problem, the board assumed an initial starting position of each piece (standard position at the start of each game), and then kept track of each piece as a square was vacated and another vacant square became occupied. Sufficient information was available for the board to figure out what had occurred. Of course, the board could be fooled if two pieces were purposely interchanged. Another problem arose if a game was to be resumed after a recess. There would have to be a means of communicating to the board where each piece was, so the board could resume keeping track of each piece. Another drawback is that these switches are generally slow. Therefore, a speed chess game probably could not be effectively recorded by such a board. There is obviously a need for a chess board which not only can keep track of a game in progress, but can identify which piece is on every square at all times as well as perform these functions faster than a person can move a piece.
U.S. Pat. No. 3,760,404 (Khlebutin) discloses a chess board which places a single coil under each playing square. A pulse of energy is fed sequentially to each coil which shock excites a resonant circuit in the chess piece located on the square selected. The coil picks up the oscillations from the piece's resonant circuit, and an analysis circuit determines the resonant frequency. Each piece has its own unique resonant frequency which allows the analysis circuit to determine the identity of the piece.
Great Britain Patent No. GB 2 103 943 (Blenkinsop, et al.) discloses two embodiments of a chess board which places coils under the playing surface of the board. In the first embodiment, a transmit coil and a receive coil are located under each square. Each square is searched sequentially. The transmit coil is energized by a short duration pulse of energy. Each chess piece contains a resonant circuit, comprising an inductor in parallel with a resonating capacitor, which produces a response on both the leading edge of the input pulse and the trailing edge of the input pulse. This is known as an impulse or shock excitation, and such an impulse contains energy at a broad spectrum of frequencies. The chess piece produces a response at its resonant frequency (corresponding to its identity), and the response is picked up by the receive coil and delivered to an analysis circuit which determines the frequency of the response and therefore the identity of the piece. Only the response to the trailing edge of the input pulse is analyzed.
In the second embodiment, a single coil is placed under each square. Each square is searched sequentially. Instead of a short duration pulse, a triangular, or ramp excitation pulse is employed since only the trailing edge is needed for the impulse excitation. The signal on the coil resulting from the piece's resonant frequency occurs after the ramp excitation has ended, thus allowing a single coil to replace the pair of coils described in the first embodiment. The single coil embodiment functions thereafter in the same manner as the first embodiment. Impulse excitation of a playing piece resonant circuit is employed as the basic technique. The trailing edge of a ramp or short pulse is used to provide the basis for the impulse. To be effective, the impulse must occur in a very short time, as well as contain considerable energy created by a large change in voltage level. The shorter the time span of the impulse, the greater its frequency spectrum; the greater the change of voltage for the impulse, the greater the energy at each frequency. The ramp or pulse is directed to a particular coil beneath a playing square on the board. The coil requires considerable inductance, which translates to many turns, in order to convert the abrupt voltage change to a high energy impulse. The coupling between the coil beneath the playing surface and the coil in the playing piece is the mechanism for transferring the impulse into the resonant circuit of the piece.
A resonant circuit is characterized by its "Q", a factor which is the ratio of output voltage to input voltage at a particular frequency. Since the input signal to the piece is an impulse which contains virtually all frequencies, it is apparent that the amount of energy at any one particular frequency is quite small. In order to produce an output signal which is strong enough to be processed for the purpose of piece identification, the "Q" of the resonant circuit in the piece must be quite high, since the input energy level at that frequency is necessarily quite small. A high "Q" requires a large inductance, which translates to many turns of wire on a ferrite core to concentrate the magnetic field produced by the current induced in the windings. The smallest number of turns of any piece, as described in the prior art, is 133, and the largest number is 185. A capacitor is connected in parallel with the coil in the piece to create a resonant circuit and is tuned to a particular frequency. When such a circuit is excited, it produces oscillations at its resonant frequency as well as at harmonics of that frequency.
In the present case, the harmonics of the frequency can be ignored, and only the "fundamental" frequency is of interest. The response from the piece resonant circuit is in the form of damped oscillations. The response is characterized by a large amplitude oscillation immediately following the impulse excitation, followed by continuously decreasing amplitude oscillations until the signals become indiscernible from noise. It is this pattern of oscillations which couple back to the coil beneath the board surface. In order to effectively process the oscillations received by the coil under the board, the analysis circuit must be blanked until such time as the original impulse and any non-linear effects of the impulse die out and the only signal remaining on the coil are the decaying oscillations generated by the piece resonant circuit.
Many problems are associated with the prior art. One such problem is the creation of a high energy impulse. For the impulse to be effective, the impulse must contain considerable energy at the frequency of each piece, in order to be able to effectively excite each piece. The impulse also contains considerable energy at other frequencies, both below and above the span of frequencies of the pieces. This energy radiates from the coil under the board and potentially interferes with other electrical and electronic apparatus in the vicinity of the board. Every country effects very strict radiation standards in order to control this type of radio frequency interference (RFI). It would be difficult and possibly impossible for a company producing a board operating on an impulse basis to obtain a license to market such a board to the general public.
In addition, the coil under the board square must contain many turns to generate the high energy impulse needed for effective operation. This restricts the minimum size of the square, and resulting size of the overall board to a board approaching tournament size, which utilizes approximately 21/4 inch squares. For a product utilizing "smart board" technology, not being able to make small chess sets is quite restrictive.
The coil in each piece must also have a high "Q" in order to generate sufficient energy at its particular resonant frequency for an analysis circuit to determine its identity. Such a coil with a large number of turns of wire wound on, for example, a ferrite form is not only expensive to produce, but cannot be made to fit into small chess pieces which would be employed on chess sets materially smaller than tournament size.
The need to couple energy between the coil under the playing surface and the coil in a piece above the board creates a positioning problem for a piece. As a piece is moved away from the center of a square, the signals coupling from one coil to the other diminish in a non-linear fashion, which is characterized by the signal level decreasing faster and faster as the piece is displaced in equal increments of distance. This causes the piece to rapidly become undetectable as the piece moves away from the center of a square. Increasing the level of the excitation signal only improves this situation slightly due to the non-linear behavior. Increasing the inductance of the coil under the board, or the "Q" of the piece circuit also has a small effect on this problem. Most attempts to overcome this problem with increased excitation only aggravates the RFI problem.
In order to uniquely determine the identity of a piece on a playing square, each square must be addressed individually, or sequentially. This adds to the number of wires that must be located beneath the playing surface, as well as the total time it takes to search for all pieces and affects the ability of the smart board to effectively handle speed chess games. This system of piece recognition has several significant drawbacks. First, the necessity to place numerous multi-turn coils below the playing surface of the board limits the minimum size of the squares on the board to approximately 2 inches (a tournament board utilizes approximately 21/4 inch squares). In addition, this type of construction is expensive, and does not lend itself to significant production cost reduction through automation. Second, when two coils are utilized beneath each square, the transmit coil couples to the receive coil even when no piece is present. This is akin to a "false alarm". Special circuits are needed to reduce the false alarms to a tolerable level. Third, the board "radiates" electrical energy into the air, with the potential of interfering with other nearby electronic equipment. By reciprocity, other nearby electronic equipment could interfere with the operation of the board. The allowable level of radiation from any electrical or electronic device (such as the "smart board" being described) is strictly regulated in every country. Before such a device can be sold, a license must be obtained, which depends in part on the device passing an electronic emission test. Finally, the physical embodiment of the circuit in each piece occupies considerable volume, is costly, and probably requires adjustment by an assembler, which in itself is expensive. Clearly, a different approach to piece recognition is needed if a cost effective, low radiation "smart board" is to become a household item.